This invention relates to a piston for a reciprocating internal combustion engine and, more particularly, to a piston of the type described having an improved piston ring construction.
The standard piston ring in practical use is a combination of three rings, namely a tip ring serving as the pressure ring which is for the purpose of preventing a phenomenon sometimes referred to as "blow-by" wherein high pressure combustion gas from the combustion chamber side of the engine flows out to the crank case side thereof, a second ring and an oil ring which reduces the consumption of oil by suppressing the amount of lubricating oil which flows into the combustion chamber side of the engine from the crank case side.
The combined ring of this standard construction was submitted to tests using a 1500 cc four-cycle engine for the purpose of measuring oil consumption (gr/h) and blow-by (l/min). In the test, referred to hereinafter as Test I, the mean values obtained were 0 gr/h, 17 l/min at 4600 rpm with a full engine load, 10 gr/h, 18 l/min at 5200 rpm with a full engine load, and 50 gr/h, 0 l/min at 2500 rpm with an engine high boost of 650 m/mHg. While oil consumption and blow-by values on this order are tolerable for practical use, it is preferable that these values be reduced to improve upon engine efficiency.
To the foregoing end, various pressure rings used in a combination of three rings have been proposed to exhibit an improved oil tightness characteristic.
However, while improvements in pressure rings have made it possible to diminish blow-by in reciprocating internal combustion engines, the piston arrangements heretofore available have not succeeded in simultaneously reducing oil consumption, as will be described later in a more detailed discussion of the prior art.